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Highlights of Recent INESC MN Publications


Graphene transfer process and AFM imaging.

"Transparent conductive graphene textile fibers"

A.I.S. Neves, T.H. Bointon, L.V. Melo, I. de Schrijver, M.F. Craciun and H. Alves


Scientific Reports 5, 9866 (2015)

Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn.

DOI: 10.1038/srep09866



"A System Based on Capacitive Interfacing of CMOS With Post-Processed Thin-Film MEMS Resonators Employing Synchronous Readout for Parasitic Nulling"

Liechao Huang, Warren Rieutort-Louis, Alexandra Gualdino, Laura Teagno, Yingzhe Hu, João Mouro, Josue Sanz-Robinson, James C. Sturm, Sigurd Wagner, Virginia Chu, João Pedro Conde, Naveen Verma


IEEE Journal of Solid State Circuits 50 (4), 1002 (2015)


Thin-film MEMS resonators fabricated at low temperatures can be processed on CMOS ICs, forming high-sensitivity transducers within complete sensing systems. A key focus for the MEMS devices is increasing the resonant frequency, enabling, among other benefits, operation at atmospheric pressure. However, at increased frequencies, parasitics associated with both the MEMS-CMOS interfaces and the MEMS device itself can severely degrade the detectability of the resonant peak. This work attempts to overcome these parasitics while providing isolation of the CMOS IC from potentially damaging sensing environments. To achieve this, an interfacing approach is proposed based on capacitive coupling across the CMOS IC passivation, and a detection approach is proposed based on synchronous readout. Results are presented from a prototype system, integrating a custom CMOS IC with MEMS bridge resonators. With the MEMS resonators fabricated in-house at 175°C on a separate substrate, readout results with multiple different resonators are obtained. In all cases, the IC enables detection with >20 dB SNR of resonant peaks that are only weakly detectable or undetectable directly using a vector-network analyzer (VNA).


DOI: 10.1109/JSSC.2014.2380440





"Pressure Effects on the Dissipative Behavior of Nanocrystalline Diamond Microelectromechanical Resonators"

J.T. Santos, T. Holz, A.J.S. Fernandes, F.M. Costa,V. Chu, J.P. Conde


J. Micromech. Microeng. 25, 025019 (2015).

Diamond-based microelectromechanical resonators have the potential of enhanced performance due to the chemical inertness of the diamond structural layer and its high Young’s modulus, high wear resistance, low thermal expansion coefficient, and very high thermal conductivity. In this work, the resonance frequency and quality factor of MEMS resonators based on nanocrystalline diamond films are characterized under different air pressures. The dynamic behavior of 50–300 μm long linear bridges and double ended tuning forks, with resonance frequencies between 0.5 and 15 MHz and quality factors as high as 50 000 are described as a function of measurement pressure from high vacuum(~10 mTorr) up to atmospheric conditions. The resonance frequencies and quality factors in vacuum show good agreement with the theoretical models including anchor and thermoelastic dissipation (TED). The Young’s moduli for nanocrystalline diamond films extrapolated from experimental data are between 840–920 GPa. The critical pressure values, at which the quality factor starts decreasing due to dissipation in air, are dependent on the resonator length. Longer structures, with quality factors limited by TED and lower resonance frequencies, have low critical pressures, of the order of 1–10 Torr and go from an intrinsic dissipation, to a molecular dissipation regime and finally to a region of viscous dissipation. Shorter resonators, with higher resonance frequencies and quality factors limited by anchor losses, have higher critical pressures, some higher than atmospheric pressure, and enter directly into the viscous dissipation regime from the intrinsic region.

DOI: 10.1088/0960-1317/25/2/02501



 “Strategies for pTesla field detection in biomedical imaging using magnetoresistive sensors with a soft pinned sensing layer”

J. Valadeiro, J. Amaral, D.C. Leitão, R. Ferreira, S. Cardoso and P.P. Freitas

 IEEE Trans Magn., 51 (1), 4400204 (2015)


The detection of low-intensity and low-frequency signals requires magnetic sensors with enhanced sensitivity, low noise levels, and improved field detection at low operating frequencies. Two strategies to improve the detectivity levels of devices based on tunnel magnetoresistive sensors are demonstrated: 1) a large number of sensors connected in series or 2) an individual sensor with a large sensing area and integrated magnetic flux guides. State-of-the-art MgO-based magnetic tunnel junctions with a soft pinned sensing layer were used in this paper. For 952 sensors in series a sensitivity of 29.3%/mT and a detection level of 455 pT/ $mathrm{Hz}^{mathrm {mathbf {1/2}}}$ were obtained at 100 Hz, whereas the integration of magnetic flux guides in a single sensor yielded a sensitivity of 138.3%/mT and a detection level of 576 pT/ $mathrm{Hz}^{mathrm {mathbf {1/2}}}$ at the same frequency. These two strategies imply a large device footprint, being suitable when a high spatial resolution is not an application requirement.


DOI: 10.1109/TMAG.2014.2352115                  



“Real-time monitoring of magnetic nanoparticles diffusion in lateral flow microporous membrane using spin valve sensors”

A.Chicharo, F.Cardoso, S. Cardoso, P.P. Freitas,


IEEE Trans Magn., 51 (1), 5100104 (2015)


This paper investigates real-time monitoring and detection of 10.5 nm magnetic nanoparticles (MNPs) (Fe3O4) flowing in a nitrocellulose (NC) membrane over two spin valve sensors. The fabricated device gives information on the concentration of MNP flowing through the NC membrane of a typical lateral flow test, and gives relevant dynamic characteristics, such as flow rate and MNP distribution on capillary-driven systems. Sensor output varies linearly with MNP concentration. Experiments show average flow rates varying from 0.2 to 0.3 mm/s depending on MNP concentration. Signal shape [V(t)] gives information on MNP spatial distribution at the particle front flowing over the sensor.


DOI: 10.1109/TMAF.2014.2358645


C:\Documents and Settings\Filipe Cardoso\Os meus documentos\Dropbox\Stuff to update\Artigos\Os meus artigos\Artigo EMSA 2014\fig4.JPG


“Magnetic counter for Group B streptococci detection in milk”

C. M. Duarte, A. C. Fernandes, F.A. Cardoso, R. Bexiga, S. Cardoso, P. P. Freitas


IEEE Trans Magn., 51 (1), 5100304 (2015)


Identification of bovine mastitis pathogens is necessary to control the disease, reduce the risk of chronic infections, and target the antimicrobial therapy to be prescribed. Development prospects for new bovine mastitis diagnosis methodologies go also through rapid and efficient devices that can offer a “cow-side” use, meaning that raw milk collected for analysis should have limited pretreatment. This paper aims at developing a magnetic counter that identifies the presence of Streptococcus agalactiae (a Group B Streptococci) in raw milk. The detection is done with an integrated microfluidic platform, where 50 nm magnetic beads attached to Streptococcus agalactiae are dynamically detected by magnetoresistive sensors. This device allows the analysis of raw milk without bridging the microfluidic channels, making this integrated platform very attractive for fast bacteriological contamination screening.


DOI: 10.1109/TMAG.2014.2359574



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